Currently some earth-working machines such as dragline excavators are designed with a multiple length boom. This boom includes removable center sections that can increase or decrease its overall length to accommodate changes in mine configuration. At the mine site, the dragline excavator generally raises its boom from its starting horizontal position to an optimum angle which defines its operating position.
These dragline excavators generally include a rotating main frame having a gantry rising upwardly to support a pivotally mounted boom by means of tension members (wire rope) running from a winch on the frame to the top of the gantry out to the point of the boom and back to the gantry. Sheaves are positioned at the boom point and top of the gantry to receive the wire rope attached to the winch. The winch reeves the wire rope around the gantry sheaves and the boom point sheaves to draw the boom up to its operating position. Upon attaining the operating position, the winch is mechanically locked to hold this boom position. Still, this apparatus for supporting the boom is susceptible to the boom slipping down due to the unreliability of the winch lock. Also, this apparatus requires a long wire rope that is expensive to manufacture, and a sheave on the boom point that adds weight to the boom, reducing the maximum payload weight rating for the dragline.
Another apparatus for raising and supporting the boom in a fixed operating position is a wire rope/sheave/pendant pin assembly arrangement. The wire rope is reeved by a winch located on the rotating frame, received around sheaves located at the top portion of the gantry structure and around sheaves attached to one end of a pin link of the pendant pin assembly. On the opposite end of the pin link is a boom support pendant that is attached to the boom point. The boom is raised until the pin link reaches the top portion of the gantry structure and is adjacent support openings in the gantry. The axis through the boom support pendant and pendant pin assembly is aligned with the centerline axis of the support openings, so that a through bore of the pin link is concentrically aligned with the support openings. A boom support pin is inserted through the support openings and the pin link through bore to hold the boom via the boom support pendant in its fixed operating position. This apparatus provides a reliable means for supporting a fixed length boom in its operating position at an optimum angle. But by varying the overall boom length at this optimum angle, the axis through the boom support pendant and pendant pin assembly is misaligned with the support openings. This results in the inability of inserting the support pin through the support openings and the through bore of the pin link. Therefore, this apparatus is inappropriate for multiple length boom earth-working machines.